U.S. Pat. No. 3,696,186 issued on Oct. 3, 1972 for a Method of Expanding Pliable Material teaches structure for expanding vinyl material which is used as an interlayer in laminating glass templets together in order to form an automotive windshield. This patent also discloses a structure for accomplishing the method described in the patent. This patent and U.S. Pat. Nos. 2,933,759 and 3,019,475 disclose methods and apparatuses for stretching a plasticized polyvinyl-butyral web used to form the interlayer of an automotive windshield. The stretching of such material is desirable when a tinted band is placed along one lateral edge of the material so that the material may be used in the formation of a tinted windshield for an automotive vehicle. More particularly, the tinted or gradient band is located at the top of the windshield in order to reduce the light transmission capability of the windshield in that area. This reduction in light transmission aids the operator of the vehicle by reducing the amount of glare he is subject to, thereby improving his field of vision.
When the gradient band windshield has both horizontal and vertical curvature, it is necessary to stretch each interlayer prior to placing it between two glass templets. This stretching is necessary so that upon lamination of the two glass templets with the interlayer, the edge of the gradient band across the windshield will appear as a straight line when the windshield is assembled in an automobile. In its stretched condition, the interlayer will have the lateral edges thereof formed into curved configurations with different arc lengths. To facilitate the manufacture of the interlayer material, the material is produced in large rolls with the lateral edges thereof in a parallel and straight condition. Many individual interlayers may be formed from one such large roll of material.
The patents mentioned above show methods and apparatuses for stretching the original continuous length of interlayer material into a stretched condition to make it acceptable for use in a laminating procedure. The apparatus of this invention is an improvement over the apparatuses known in the prior art in that the present apparatus assures that a maximum yield is achieved from the roll of material being stretched.